Problems with Knife edge/hover
 

I just finished a new BalsaUSA 1/4 scale Fokker DR-1 Triplane. I t has a Zenoah G23 on it running gas. I cannot get the plane to do a sustained knife edge for more that a second. Do I need more rudder area? I also cannot get it to hover for more than 2 seconds until it wants to do a sustained tail slide. What size prop is best to hover with this engine? I'm using a Controlaire 4 channel reed radio. Would upgrading the radio help? Thanks. Mike